Monstrous Nightmare (5e Creature)
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Huge dragon, unaligned
Saving Throws Str +12, Dex +10, Con +11, Wis +10
Aggressive. As a bonus action, the nightmare can move up to its speed toward a hostile creature it can see.
Self-Immolate. As a bonus action, the nightmare lights itself on fire, along with anything it is wearing or carrying, for 1 minute. While on fire, a target within 5 ft. of the nightmare takes 24 (7d6) fire damage, which the nightmare is immune to. If the target is a creature, it must make a DC 20 Constitution saving throw or take 24 (7d6) fire damage on a failed save and half as much damage on a successful one. The nightmare cannot use this feature again until after a short or long rest.
Rampage. When the nightmare reduces a creature to 0 hit points with a melee attack on its turn, the nightmare can take a bonus action to move up to half its speed and make a bite attack.
Reckless. At the start of its turn, the nightmare can gain advantage on all melee weapon attack rolls it makes during that turn, but attack rolls against it have advantage until the start of its next turn.
Relentless (Recharges after a Short or Long Rest). If the nightmare takes 14 damage or less that would reduce it to 0 hit points, it is reduced to 1 hit point instead.
Wounded Fury. While it has 10 hit points or less, the nightmare has advantage on attack rolls. In addition, it deals an extra 7 (2d6) damage to any target it hits with a melee attack.
Multiattack. The nightmare makes two bite attacks.
Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 18 (2d10 + 7) piercing damage. Instead of dealing damage, the nightmare may grapple a target, if it is Huge or smaller.
Fire Burst (Recharges 5-6). The nightmare exhales fire in a 30 by 5-foot line. Each creature in that area must succeed a DC 20 Dexterity saving throw or take 42 (12d6) fire damage, or half as much damage on a successful one.
Wind Blast (Recharges after a Short or Long Rest). The nightmare beats its wings. Each creature within 10 feet of the dragon must succeed a DC 20 Dexterity or take 16 (2d8 + 7) bludgeoning damage and be knocked prone.
Swallow. The nightmare makes one bite attack against a Medium or smaller target it is grappling. If the attack hits, the target is also swallowed, and the grapple ends. While swallowed, the target is blinded and restrained, it has total cover against attacks and other effects outside the nightmare, and it takes X (4d6) acid damage at the start of each of the nightmare's turns. A nightmare can have only one creature swallowed at a time.
Unbridled Fury. In response to being hit by a melee attack, the nightmare can make one melee weapon attack with advantage against the attacker.
Of all the lesser dragon-kin, one of the most ferocious and savage is the aptly named Monstrous Nightmare. It is similar to a large wyvern, with a serpentine neck and tail, and a low profile, crawling on its wings when not in flight. They have large horns sprawling from the backs of their heads, which vary in size with age, and two rows of large spines from the base of their neck all the way down to the tip of their tail, both serving the purposes of visual display. These dragons easily reach lengths of 60 feet, as well as a 68-foot wingspan and 5000 lbs. weight, and are well known for their pension for aggression, stubbornness, and fury, with most warriors hesitant to go up against them.
Hot Headed. Forests inhabited by Monstrous Nightmares are some of the most dangerous places for commoners to travel through, as they are incredibly territorial and proud dragons. Males, in particular, will fight to defend their territory, even going so far as to protect the offspring of females that are not theirs as males will kill them to mate with the female. This shows a rarely seen softer side of these dragons, often overshadowed by their ferociousness.
Torchlight Tutor. Despite their fearsome reputation, as stated earlier Nightmares do have a softer side, which means they can be trained by humanoids. As with between fellow warriors, the relationship between a Nightmare and its rider is based on mutual respect: while this may seem like suicide, a good way to start training is to gently place one's hand upon the dragon's snout, and show they're not a threat. Feeding time, as with many animals is bonding time and Nightmares are, to many new riders' surprise, omnivores, allowing for a wide selection of choice feeds, with corn, crab, fish, mutton, and wild boar being special favorites. Be aware when considering training a Monstrous Nightmare, however, that they are proud and stubborn, making them hard to control and very disobedient, in addition to just being easily distracted by things as small as butterflies and flowers.